Packet-based telecommunications networks typically include media gateway devices. For example, a Session Border Controller (SBC) is deployed at the border of a Voice Over Internet Protocol (VoIP) network and protects the network by policing communication sessions such as voice calls (or ‘VoIP calls’) flowing into or out of that network. The SBC may have to relay media data for a communication session, for example either because the media data transits the protected network and needs policing, or because the originating and terminating endpoint devices for the communication session cannot send media data to each other directly as they are located in different private networks.
Communication sessions such as voice calls are commonly set up using the Session Initiation Protocol (SIP). A SIP session involves an offer stage requesting setup of a communication session and an answer stage responding to the setup request. The offer stage involves one or more communication session setup request messages in the form of SIP signaling messages being transmitted from an originating endpoint device to a terminating endpoint device. The communication session setup request messages frequently traverse a number of media gateways en-route, each of which may redirect or forward the communication session setup request messages. The answer stage involves one or more communication session setup response messages being transmitted in the opposite direction from the terminating endpoint device to the originating endpoint device in order to accept or reject the communication offer.
Communication session setup request signaling messages typically carry a single description of the media parameters for the communication session, including an offered address where media data from the request receiving device should be transmitted.
This presents a problem for a media gateway processing a communication session setup request because the media gateway does not know, before the completion of the communication session setup process whether it would be best to relay media data for the communication session via the media gateway or not.
A media gateway will typically choose to relay the media for the communication session, since that is the ‘safe’ option. The disadvantage of selecting the ‘safe’ option is that it forces the media data to be relayed through every media gateway in the communication session setup path, which wastes valuable network resources and degrades the media quality by increasing latency.
It would therefore be desirable to provide improved methods for controlling establishment of media paths for communication sessions in a telecommunications network.